Answer
You should decrease the price of museum admission in order to increase total revenue.
Work Step by Step
Going to a museum is a luxury and not a necessity, so the demand for museum tickets will be elastic, as people enjoy going to museums but do not depend on museum visits as a basic human need (say, like visits to the doctor). Therefore, you should decrease the price of admission, as a decrease in price will cause an increase in quantity demanded that is greater in magnitude. Therefore, knowing that total revenue is calculated as $P\times Q$, we know that a decrease in price and an increase in quantity demanded that is greater in magnitude will increase total revenue mathematically.
